1. Field of the Invention
The invention relates to an image forming system, a sheet treating apparatus, an image forming apparatus, a control program and a storage medium.
2. Description of the Related Art
Generally, a sheet treating apparatus connected to an image forming apparatus is used for the punching process to a sheet having an image formed thereon by the image forming apparatus. In this sheet treating apparatus, a sheet discharged from the image forming apparatus is conveyed to a punch unit along a predetermined conveying path, and punching is effected on the sheet by this punch unit. When punching is to be effected by the punch unit, use is made of a method of once stopping the conveyance of the sheet and effecting punching on the sheet, or a method of effecting punching while conveying the sheet. In any of these methods, at a position on this side of the punch unit, a side edge portion of the sheet is detected by a sensor or the like, and the widthwise positioning of the punch unit is effected.
As this positioning method, there is, for example, a method of detecting the side edge portion of the sheet, and thereafter moving the punch unit to a position conforming thereto, and effecting punching. Also, the relative position of the sensor and the punch unit is predetermined in accordance with the size of the sheet, and the sensor and the punch unit are constructed integrally with each other, and there is a method of effecting punching at the timing whereat the sensor has detected the side edge portion of the sheet.
Here, during the conveyance of the sheet from the sheet supplying cassette of the image forming apparatus to the punch unit of the sheet treating apparatus via the image forming apparatus, or by a change or the like of the sheet supplying cassette, the sheet may sometimes deviate from a reference position into a sheet width direction (a direction orthogonal to the conveying direction of the sheet). Consequently, the position of the current sheet and the position of the next sheet may sometimes deviate with respect to the sheet width direction. In order to cope with this positional deviation of the sheet in the sheet width direction, there is an apparatus which detects the side edge portion of each sheet, and moves the punch unit in the widthwise direction of the sheet to thereby effect the positional adjustment of the punch unit in the sheet width direction (see Japanese Patent Application Laid-open No. 2001-97638). In order to effect such positional adjustment, the sensor and the punch unit are once retracted to a position separate from the side edge of the sheet, and start to move from the retracted position in order to detect the side edge portion of the sheet.
However, the above-described positional adjustment of the punch unit in the sheet width direction for coping with the positional deviation of the sheet in the sheet width direction is effected each time a sheet is carried into the punch unit and therefore, it is limited in further improving the productivity of the punching process, and further is limited in improving the throughput of an entire image forming system including the sheet treating apparatus.